# https://blender.stackexchange.com/questions/79595/change-diffuse-shader-to-emission-shader-without-affecting-shader-color

"""
replace diffuse cycles material nodes with emission cycles material nodes that preserve the color
"""

import bpy

def replace_with_emission(node, node_tree):
    new_node = node_tree.nodes.new('ShaderNodeEmission')
    connected_sockets_out = []
    sock = node.inputs[0]
    if len(sock.links)>0:
        color_link = sock.links[0].from_socket
    else:
        color_link=None
    defaults_in = sock.default_value[:]

    for sock in node.outputs:
        if len(sock.links)>0:
            connected_sockets_out.append( sock.links[0].to_socket)
        else:
            connected_sockets_out.append(None)

    #print( defaults_in )

    new_node.location = (node.location.x, node.location.y)

    if color_link is not None:
        node_tree.links.new(new_node.inputs[0], color_link)
    new_node.inputs[0].default_value = defaults_in

    if connected_sockets_out[0] is not None:
        node_tree.links.new(connected_sockets_out[0], new_node.outputs[0])


def material_diffuse_to_emission(mat):

    doomed=[]
    for node in mat.node_tree.nodes:
        if node.type=='BSDF_DIFFUSE':
            replace_with_emission(node, mat.node_tree)
            doomed.append(node)

    # wait until we are done iterating and adding before we start wrecking things
    for node in doomed:
        mat.node_tree.nodes.remove(node)


def replace_on_selected_objects():
    mats = set()
    for obj in bpy.context.scene.objects:
        if obj.select:
            for slot in obj.material_slots:
                mats.add(slot.material)

    for mat in mats:
        material_diffuse_to_emission(mat)

def replace_in_all_materials():
    for mat in bpy.data.materials:
        material_diffuse_to_emission(mat)


if True:
    replace_on_selected_objects()
else:
    replace_in_all_materials()